RSV causes severe lower respiratory tract disease in infants and small children worldwide and it is estimated that more than 90,000 hospitalizations of RS infected children occur annually in the US. No vaccine is licensed yet and no effective antiviral therapy is available for routine use. Understanding virus biology and the regulation of viral replication often provides inforamtion that can be utilized to develop products either of preventive or of therapeutic luse. RSV has a non-segmented negative-sense RNA as the genome and encodes two non-structural proteins, the NS1 and NS2. Previously, short-lived CTLs were detected against NS2 of these proteins in RSV infected humans. CTL response is one of the important immunological mechanism for virus clearence during RSV infection. It would be of importance if we can improve the effective CTL response by manipulating the peptides that are involved. The secondary and tertiary structures of the NS2 peptides will be determined and an effort to correlate the structure with function, i.e. CTL responses will be made. My previous stuides inducated that the NS1 is a potent inhibitor of RSV model genomes and probably acts as a negative regulator of viral replication. In the current project, I would like to define the biochemical basis of this negative replication in (a) in vitro transcription and replication system and (b) in vivo system in which either complete expressed proteins or overlapping peptide fragments will be tested for their inhibitory potential. New biologics, agents that boost cell-mediated virus-clearnence or antiviral peptides to curb virus replication would be of immense use to manage virus infections where prevention of infection is not possible. The newly found functional roles of some of the naturally occuring viral gene products might be exploited to develop such useful technologies either with prophylactic or therapeutic indications. In addition, characterization of these peptide and protein sequences will be useful in improving recombinant viral vaccines to produce most effective immunological responses. The knowledge and information gained in these studies will be used to review the INDs and product licensing applications.